The standards development organization 3GPP (The 3rd Generation Partnership Project) has promoted standardization of LTE-Advanced (Long Term Evolution Advanced: LTE-A) as next-generation wireless communication standards compatible with LTE (Long Term Evolution). The LTE-A has examined a wireless IF (Interface) for efficiently covering a local area of indoor facilities etc. in which a high volume of traffic is intensively generated in addition to cell arrangement centered on a conventional macrocell. With this, a heterogeneous network (HetNet) in which a low transmission power cell (also called an “LPN (Low Power Node)”) such as a pico-cell or a femto-cell is arranged inside a macrocell has been examined. A HetNet environment will hereinafter be described using the pico-cell as the low transmission power cell.
The HetNet environment is provided with a macrocell base station for building a macrocell, and a pico-cell base station for building a pico-cell inside the macrocell. In addition, frequencies respectively used by the macrocell base station and the pico-cell base station are desirably the same in view of efficient use of the frequency in the HetNet environment. Since the macrocell base station covers a range wider than the pico-cell base station, its load is relatively high. Consequently, a load of the macrocell base station is desirably distributed to the pico-cell base station in order to reduce the load of the macrocell base station in the HetNet environment.
One art for implementing load distribution of the macrocell base station includes “Range Expansion” (see Non-patent Reference 1). FIG. 16 is a diagram conceptually showing the technical contents of “Range Expansion”. According to this art, a wireless terminal (UE: User Equipment) connected to a pico-cell located in the pico-cell edge periphery maintains connection to the pico-cell, or UE connected to a macrocell is actively connected to a pico-cell. That is, in order to give priority to connection between the UE and the pico-cell, an area in which the UE is connected to the pico-cell is expanded by applying an offset to downlink reception quality of the pico-cell. However, the UE connected to the pico-cell or the UE in which connection to the pico-cell is maintained by the art greatly suffers interference between cells from the macrocell in the environment in which each of the macrocell and the pico-cell uses the same frequency.